Field of the Invention and Related Art Statement
This invention relates to an ultrasonic diagnostic apparatus having an ultrasonic vibrating element arranged in an inserting portion thereof to scan an object to be inspected in order to obtain an ultrasonic image of the object, and more particularly, to an ultrasonic diagnostic apparatus having an endoscope by which an optical image of the object can be also obtained.
In the ultrasonic diagnostic apparatus, there are provided the ultrasonic vibrating element at a distal end of the inserting portion and a rotator to scan the object with the ultrasonic wave generated by the element in the direction that crosses at right angles with respect to the center axis of the inserting portion. A cover is arranged to surround the rotator, which serves as a window through which the ultrasonic wave transmits, and the space formed between the rotator and the cover is filled with an ultrasonic propagating medium such as water and liquid paraffin.
In Japanese Utility Model Publication Kokai Sho No. 58-136,106, there is disclosed a known ultrasonic diagnostic apparatus. FIG. 1A is a cross-sectional view showing a distal end portion of an inserting portion of the conventional ultrasonic diagnostic apparatus, FIG. 1B is a front view thereof and FIG. 1C is a cross-sectional view showing the section cut along A--A line in FIG. 1A. As apparent from these figures, the conventional ultrasonic diagnostic apparatus is formed as so-called forward view type, therefore a center axis y of a rotator 3 serving as a mirror on which an ultrasonic wave emitted from an ultrasonic vibrating element 2 is reflected, is deviated from a center axis x of the inserting portion of the apparatus, and there is provided an observing optical system 1 beside the rotator 3. A cover 4 surrounding the rotator 3 also forms a part of the circumferential surface of the inserting portion and a portion of the cover constitutes a window through which the ultrasonic wave reflected by the mirror 3 exits and ultrasonic wave reflected by the object is made incident upon the mirror.
Such conventional ultrasonic diagnostic apparatus has the following problems. That is to say, since the circumferential surface of the cover 4 also serves to form the circumferential surface of the inserting portion, the center axis of the curvature of the cover is coincident with the center axis x of the inserting portion but is deviated from the center axis y of the rotator 3. Under such construction, the distance between the cover 4 and rotator 3 (reflecting mirror), and the incident angle of the ultrasonic wave with respect to the cover 4 vary in dependent on a point of the cover 4 where the ultrasonic wave exits and enters from and into the inserting portion. FIG. 1D is a schematic view illustrating an ultrasonic image displayed on a screen of a monitor formed by the conventional ultrasonic diagnostic apparatus. As shown in FIG. 1D, in case the ultrasonic wave propagates through the cover 4 in an area 5, where the incident angle would be not so large, there is no undesired artifact (multiple echo) and a high azimuth resolution can be obtained. But, in case the ultrasonic wave propagates in an area 6, where the incident angle would be large, there is recognized artifacts 7 caused by refraction and reflection of the ultrasonic wave, and the azimuth resolution becomes low. For example, the circular-shaped object is indicated as an elliptical 8 on the monitor due to the refraction of the ultrasonic wave. In FIG. 1D, the numerical number 9 represents the circumference surface of the cover 4 and the numerical number 10 represents a normal artifact.
Contrary to the above, in a specification of U.S. Pat. No. 4,572,201, there is disclosed an ultrasonic diagnostic apparatus in which the center axis of the curvature of the cover surrounding the rotator is arranged to be coincident with the center axis of the rotator. FIG. 2 is a cross-sectional view illustrating the distal end of the inserting portion of this apparatus. However, in this apparatus, a central axis of the inserting portion, the rotating axis of the rotator 3 and the center axis of the curvature of the cover 4 are arranged on the same axis, as clear from FIG. 2. In the inside of the inserting portion of the apparatus, it is necessary to arrange a light guide 1a constituting the illuminating system and an image guide 1b constituting the observing system (or a signal cable in case that a solid state image sensor is used), these elements extending from the distal end of the inserting portion to an operational portion of the apparatus, besides a shaft 3a extending from a rotator 3 on which an ultrasonic element 2 is provided to a sub-operational portion. In this case, since the shaft 3a is coincident with the rotating axis of the rotator 3, there would be formed a wasteful space in which the light guide 1a and the image guide 1b are not arranged, and the outer diameter of the inserting portion of the apparatus as a whole becomes thick. Thus, there :s a drawback that the inserting portion cannot be inserted into a cavity of living body easily.
Further, in case that the observing system comprises a solid state image sensor, it is necessary to arrange two signal cables, one of them is extended from the solid state image sensor and the other is extended from the ultrasonic element, both of which are connected to an external controlling device v-a the operational portion of the apparatus. However, since these two cables of the conventional apparatus are arranged so closely to each other in the inserting portion, when the solid state image sensor and the ultrasonic element are driven at the same time they would be influenced by each other and the inductive noises are generated in both cables. Therefore, there are appeared noises on one or both of the optical image and ultrasonic image displayed on the screen of the monitor and highly qualified images cannot be obtained.